The Generation of Available Potential Energy by Latent Heat Release in a Mid-latitude Cyclone

The theory of available potential energy applied to a “translating” atmospheric volume is used to estimate the generation of available potential energy for the cyclogenetic, mature, and occluding stages of a mid-latitude cyclone. Primary attention is focused upon the importance of the diabatic process of latent heat release in generating the storm’s available potential energy. In addition, preliminary estimates for the process of infrared cooling are presented. Total latent heat release is determined from observed precipitation rates. Three different models for the vertical distribution of latent heat release together with the storm’s structure provided by isentropic analyses are utilized to estimate the contribution by latent heat release to the available potential energy of the disturbance. For each stage of the storm, variations in the generation estimates betw-een models were extremely small. For the cyclogenetic, mature, and occluding stages, generation estimates of approximately 1, 8, and 6 W m--2, respectively, reflected changes in the horizontal distribution of precipitation about the storm. Two simplified cooling distributions werc assumed to evaluate the importance of infrared cooling in the generation. The first was one of uniform cooling a t the rate of 1.4T day thoughout the volume, and the second was one in which the clear air was cooled at a greater rate than the cloudy air. Positive generation estimates on the order of 1 to 2 W m-2 resulted from these calculations. The results of this study indicate that the diabatic process of latent heat release is very likely an important factor in the subsequent behavior of the system. It is speculated that an energy supply of this magnitude, available for immediate conversion to kinetic energy, is sufficient to offset a major portion of the storm’s frictional dissipation. Generation estimates for the process of infrared cooling, while less reliable than those for latent heat release, indicate that this process also contributes to the storm’s available potential energy supply.